BY J. P. HILL. 73 



what we have described* in the development of an individual Cysti- 

 cercoid in Pohjcercus. And I may here add that our observations 

 on the development of the Cysticercoid in Folycercus Didtjmo- 

 yasti'is strikingly confirm Villot's view that the position of the 

 head in Cysticercoids of the type of Cysticercus arionis is the 

 primitive one and not secondary as Leuckartf believes. 



When the Cysticercoid is examined in the fresh condition, it is 

 seen to possess numerous uniformly diffused calcareous corpuscles 

 •Ol-*012mm. in diameter. At one end, the anterior, is a slight 

 depression indicating the aperture of evagination of the head. 



In sections the three parts found in all Cysticercoids of this 

 type can be readily distinguished.! These parts are: (1) the 

 head, (2) the body, (3) the caudal vesicle. The head forms a 

 somewhat conical mass lying invaginated in the body, and with 

 the blunt apex of the cone pointing to the aperture of evagination 

 of the head. It bears on its sides four large and well-marked 

 suckers, and in its centre lies the retracted rostellum, the anterior 

 end of the latter forming the l)lunt apex of the head. 



The head is covered by a definite cuticle and is composed of a 

 dense mass of small-celled tissue. The suckers are composed of 

 rounded cells, radial and circular fibres not being recognisable. 



The rostellum is stout, thickest in its middle region, and with 

 blunt anterior and posterior ends. It extends to near the pos- 

 terior end of the head, terminating on a level with the posterior 

 border of the suckers. It is composed of rounded cells larger and 

 clearer than those of the rest of the head. Surrounding it is a 

 thin sheath of a cellular nature, apparently corresponding to the 

 muscular receptacle of other forms (cf. Polycercus Didymogastris)^ 

 but distinct muscular fibres were not recognisable in it. At the 

 anterior end of the rostellum are -the small hooks, sixteen to 



* P.L.S.N.S.W. 2nd Series, Vol. viii. p. 365. 

 t Loc. cit. p. 362. 

 t Villot, " Metamorphoses des Tenias des Musaraignes," Ann. des Sci. 

 Nat. (6), T. viii. 1878, p. 5. 



